Why Thomas Hunt Morgan was honored with the Nobel Prize in the year 1933?

Thomas Hunt Morgan was an American biologist and geneticist, and was born on 25th Sepember, 1866 in Lexington, Kentucky. And, he won the Nobel Prize for Medicine in the year 1933 for his contribution in understanding the role that chromosome plays in heredity. He also wrote 22 books and 370 scientific paper before he died on 4th December, 1945.